It's kind of foolish to not use atonement on bosses that have some sort of increased damage mechanic (a la H stone guard, elegon, garalon, mel'jarak, amber shaper, H lei shi--might be forgetting some). But IMO there is nothing wrong with not using atonement in situations where it doesn't provide a measurable advantage compared to regular healing.

You also have to factor in the contribution you make to the raid by simultaneously contributing extra DPS while healing at the same time, and on fights like the ones specifically mentioned earlier atonement actually causes your healing #'s to be quite high while you are DPSing.

Yeah, I'd say it's stupid not to in 10 man. It's very efficient, it's a smart heal, and the damage you do can be pretty significant. There are a couple fights where you're pretty much only dpsing for Archangel (Tsulong for example), but on most fights Atonement should be one of your top heals. It's less useful for 25 man, but you still want to be doing it for Archangel at the very least.

It's probably the most boring thing in this game, right next to dpsing as a rogue.

Btw, unless you got tons of haste and crit (I don't, so I can't try it), i'm not sure it's viable. Coz with my 485 priest, N Spirit Kings is probably the only fight where i can do more than just keep my Evangelism stacks up. And I don't think i'm less skilled than anyone at pressing 3 buttons so as to get the most of my smite glyph^^

In 25man h elegon it's 40% of my healing, but there are fights in which I don't use atonement much at all, just for archangel. Like everyone has said, you can live without it, but it's nice, specially in fights in which people are spread around everywhere or have long lulls in healing.

If i rather just wanna all out heal and NOT dps in atonement, Is this considerd "stupid" for a disc pve priest? Im wondering.

mind that you can healhealheal and very occasionally cast holy fire or smite (i wouldnt call occasional casts 'dpsing'). just to build stacks. just to have archangel. just to add +25% to your 'all out heal'
what would be the reason to pass on such a buff? ^^

Not using atonement to at least build archangel is simply gimping you and the raid massively. However, on certain fights atonement is pretty much the best way to heal even outside of that (especially on 10 man), penance and holy fire are very strong, both in output and mana efficency. Smite is significantly worse but still almost (targetted, grace and ss might give heal some use, some day) outright superior to things like heal (quicker, better output, ~same mana efficency) while adding dps.

I'd argue that atonement should be topping your logs for several fights this tier. If you can heal a fight with primarly atonement you heal it with primarly atonement, the added dps is great. That this playstyle is boring as fuck is a different matter.